The most common form of packaging for electronic devices such as IC devices is a plastic housing. Typically, the electronic components are assembled on a metal leadframe and a polymer is molded over the assembly to encapsulate the device. The leadframe serves not only to support the electronic components, but has metal tabs that extend from the overmolded plastic and provide a means to electrically connect to the encapsulated electronic components.
The leadframe, prior to assembly and encapsulation, typically is square or rectangular and has a center paddle to which a semiconductor chip is die bonded. The leads that provide electrical interconnection extend from the sides of the paddle, usually along two opposing edges of the leadframe, as in the common dual-in-line package (DIP). In high pin-count packages, such as quad flat packs, leads may extend from all four sides.
In plastic overmolded packages with many leads per side, the plastic flows around the leads and forms a very integral structure. A leadframe with 10 leads per side for example provides 9 spaces where the plastic joinswever, If the same space is occupied by only three leads for example, only two spaces where the plastic joins are provided. Thus as the number of leads are reduced, the mechanical integrity of the package may become an issue.